The one difference between the Kindle Paperwhite and all the other front-lit e-readers that is a nailed on certainty is the capacitive screen on the PW compared to the infra red screen on all the others. So it seems likely that it's not the light diffuser tech that is the issue alone, instead how the light diffuser and capacitive screen layer work together.

That could be wrong, but it would explain why others don't have the same issue, instead of it just being an issue with the light diffuser tech?